Method of and apparatus for separating lightweight (aerated) concrete elements

ABSTRACT

Apparatus for separating a stack of adhering lightweight concrete elements comprises upper and lower pairs of mutually opposite elongate clamping units, the units of each pair being mounted for generally horizontal relative clamping movement toward each other so that the two pairs can grip adjacent elements in the stack. At least one clamping unit, preferably in the upper pair, is mounted for movement normal to the clamping direction so as to pivot the upper element relative to the adjacent lower element and separate these elements. This unit, and preferably all the units, comprises a multitude of single clamping jaws arranged for individual and independent movement in the clamping direction so as to compensate for possible irregularities in the elements of the stack. The clamping jaws are carried by pivotally mounted arms, the arm being pivotally mounted on a vertically movable carrier so that the clamping jaws can be moved downwardly to effect separation of all elements in the stack. This avoids the necessity of removing an upper separated element before the next lower element can be separated. A method of separating the elements comprises the described operation of this preferred apparatus embodiment.

United States Patent 1 Hasselgren et al.

[ Sept. 18, 1973 METHOD OF AND APPARATUS FOR SEPARATING LIGHTWEIGHT(AERATED) CONCRETE ELEMENTS [75] Inventors: Borje Hasselgren, Taby;Wilhelm Sehardt, Bromma, both of Sweden [73] Assignee: IntongAktieholag, Hallabrottet,

Sweden [22] Filed: Feb. 24, 1972 [21] Appl. No.: 229,057

[30] Foreign Application Priority Data Feb. 24, 1971 Sweden 2352/71 [52]US. Cl. 29/200 D, 29/427 [51] Int. Cl... B281) 13/04, B23p 19/00, B23p19/02 [58] Field of Search 29/200 D, 427, 200 R, 29/426; 2l4/8.5 R, 152

[56] References Cited UNITED STATES PATENTS 3,651,554 3/1972 Herbert29/200 D X Primary Examiner-Th0mas l-l. Eager Attorney-Roberts B. Larsonet a].

[57] ABSTRACT Apparatus for separating a stack of adhering lightweightconcrete elements comprises upper and lower pairs of mutually oppositeelongate clamping units, the units of each pair being mounted forgenerally horizontal relative clamping movement toward each other sothat the two pairs can grip adjacent elements in the stack. At least oneclamping unit, preferably in the upper pair, is mounted for movementnormal to the clamping direction so as to pivot the upper elementrelative to the adjacent lower element and separate these elements. Thisunit, and preferably all the units, comprises a multitude of singleclamping jaws arranged for individual and independent movement in theclamping direction so as to compensate for possible irregularities inthe elements of the stack. The clamping jaws are carried by pivotallymounted arms, the arm being pivotally mounted on a vertically movablecarrier so that the clamping jaws can be moved downwardly to effectseparation of all elements in the stack. This avoids the necessity ofremoving an upper separated element before the next lower element can beseparated. A method of separating the elements comprises the describedoperation of this preferred apparatus embodiment.

16 Claims, 8 Drawing Figures PATENTED SEPI 8 I973 SHEET 1 UF 7 PATENTEDSEP] 8 I975 SHEET 3 0F 7 PATENTEDSEPI ems 758 34 sum 6 0F 7 VPATENTEDSEPI 8 m3 SHEET 7 BF 7 lllll lllllllllll I ll- METHOD OF ANDAPPARATUS FOR SEPARATING LIGHTWEIGHT (AERATED) CONCRETE ELEMENTS FIELDOF THE INVENTION This invention relates to a method of and apparatus forseparating lightweight concrete elements.

BACKGROUND AND SUMMARY OF THE INVENTION Lightweight concrete productsmay be produced in the following way: Down into a casting mould alightweight concrete-forming mass is poured which, having been madeporous by means of gas generating or foaming agents for instance, isbrought to bind or harden into a semiplastic more or less cheese-likeconsistency. The casting mould mentioned frequently consists of aparallelepipedon-shaped box open upwards which advantageously may havethe length 600 cm, the width 120 cm and the height 60 cm. This meansthat the mass cast will have its plane or its large surface orientedhorizontally. When the mass, as has been said, has bound into a block ofsemiplastic self-bearing consistency, this block is raised on its edge,i.e. is turned by 90 so as to get its large surface oriented vertically,and, after that, it is subjected to a dividing procedure, preferably bybringing wires, operating horizontally as well as vertically, to passthrough the block, thus cutting it up. This dividing of the block mayproceed in almost an unlimited number of ways. The raised block may e.g.be divided by horizontal cuts only into four elements measuring 600 X 60X 30 cm or six elements measuring 600 X 60 X 20 cm and so on. But it ispossible, too, by the so-called dimension change, to divide the blockinto elements of quite different dimensions and ranges of application.The dimension change may be carried out by making one or more slots inthe block, into which slots cutting frames of varying wire distributionare then brought in. Elements of many dimensions are of course possibleto produce e.g. by arranging two or more slots for the dimension change.Finally the divided block is brought into an autoclave to be cured bymeans of steam and to obtain its final strength.

After the curing is finished, the cuts dividing the block into singleelements, may most closely be characterized as crack indications. Thisis due to a phenomenon which is here called adhesion and implies thatthe elements stick to each other strongly enough to prevent them frombeing separated without anything further. The adhesion is particularlymanifest in the downmost cuts of the block where, as is natural, theweight of the block itself provides an extra pressing-together of theelements. Within the lightweight concrete technique there have appearedmany methods and devices for the separating of lightweight concreteelements sticking together in the said way.

Thus, through the Swedish Patent No. 164 138 a device is known whichcomprises one upper and one lower pair of mutually opposite longishclamping units arranged to hold or to grip like tongs each its own oftwo lightweight concrete elements situated on either side of a dividingslot, one clamping unit of the upper pair being movable vertically oracross the clamping direction to provide a swinging of one elementrelatively to the other so as to separate the elements from each other.More strictly spoken both units of the upper pair together form an upperframe box and those of the lower pair, likewise, a lower frame box,whereby one clamping unit of each pair has the shape of a rigid pressureplate covering all the length of the block and movable to and from theopposite unit, by means of hydraulic cylinders for instance. The frameboxes are hinged mutually, affording the possibility of swinging theupper one relatively the lower one by means of special vertically actingpressure boxes. This device worked satisfactorily inasmuch as theseparating, as a consequence of the swinging movement, proceeded easilyand smoothly. Those investigations, however, which have lead to thepresent invention, sometimes revealed crack formation and othernon-desirable damages in elements separated by means of the device inquestion. The reason for that has proved to be the fact thatunevennesses, be they ever so small, in the sides of the elements causethe relatively great forces emanating from the straight and longishpressure plates to act unevenly along the sides of the elements,pressure strain thus occurring locally. Another disadvantage of thedevice is that it involves the necessity of removing each element fromthe block immediately after the separation, by means of a liftingstirrup for instance, and bringing it onto a piling pallet or otherplace of storing. This means complicated and extremely slow separatingoperations. The present invention refers to a method which lacks thedisadvantages described above and, besides, has several advantages ascompared to earlier known methods within the field. Characteristic ofthe method invented is that the elements are held by pairs of clampingunits of which at least one in each pair consists of a multitude ofsingle clamping jaws which when clamping, are brought to moveindividually or independently of each other towards the oppositeclamping unit of the pair, the jaws of at least one unit during theseparating operation being brought to move together or simultaneouslyacross the clamping direction.

Additionally, the invention also refers to a separating device forpracticing the method. Characteristic of this device is that at leastone of the units in the upper as well as in the lower pair of clampingunits consists of a multitude of single clamping jaws arranged formoving individually or independently of each other towards the oppositeclamping unit during the clamping procedure, and in that the clampingjaws of at least one clamping unit are movable together orsimultaneously across the clamping direction for bringing-about saidseparating of the elements. Other distinctive features and advantagesare seen from the attached claims. The expression lightweight concreteelements in this connection firstly refers to elements of aeratedconcrete or foam concrete, i.e. kinds of concrete obtained by using gasproducing or foaming agents respectively, but it is of course alsopossible to adapt the invention to every other kind of lightweightconcrete afflicted with problems of sticking.

With reference to the attached drawings a detailed description is givenbelow of a preferred embodiment of the invention as an example. In thedrawings FIG. 1 is a longitudinal partly sectional assembly view of thedevice on a first scale, FIG. 2 a somewhat enlarged cross section ll llof FIG. 1, FIG. 3 a still more enlarged cross section of the most vitalpart of the device, FIG. 4, 5 and 6 show partly sectional vertical viewslV IV, V V, and VI Vl respectively of FIG. 3 and FIG. 7 an extremelyenlarged detail of the device. FIG.

8 provides a strongly schematic plan view of a plant including theseparating device.

In the Figures, 1 is the general designation of a lightweight concreteblock resting on a support 2 which may be carried by wheels forinstance. In this case the block is shown divided up into two differentparts or piles 3 and 4 by a dimension change slot 5, the first pile 3 inits turn having been divided into six longish elements 6 by means ofhorizontal cuts 7 having the nature of indications, whereas the otherpile 4 has been divided into several elements 8 by horizontal as well asvertical cuts marked 9 and 10 respectively.

The invented device comprises a stationary stand with the generaldesignation 1 l, composed of a number of vertical columns 12,longitudinal beams 13 and cross beams 14. The beams together form aframe structure resting on the columns. In the frame structure 13 14there is a carrier 15 suspended which in its turn carries one pair ofupper clamping units 16 and 17 and one pair of lower ones 18 and 19. SeeFIGS. 2 and 3. In accordance with the invention these clamping unitsconsist of a great number of single clamping jaws, in FIG. 1 marked witha z.

To explain more clearly how the clamping jaws cooperate with the carrier15 special reference is made here to FIGS. 3 6. From these Figures it isseen that all the clamping jaws of units 16 19 are situated each on thelower end of one of the equally numerous arms 20, 21, 22 or 23respectively, which are essentially vertical. Thus the upper clampingjaws l6 and 17 belong together to those arms which are here called upperarms 20 and 21, while the lower clamping jaws 18 and 19 belong togetherto the arms 22 and 23 here called lower arms. These arms all arepossible to swing or move around shafts or shaft pivots orientedhorizontally or parallelly to the longitudinal direction of the carrier.Turning of the arms is carried out in this case by means of telescopicbars 24 and 25 the former of which via hinges 26 mutually connects theupper arms 20 and 21 while the latter one via hinges 27 connects theupper ends of the lower arms 22 and 23 to each other. The telescopicbars may suitably consist of hydraulic cylinders encompassingreciprocating pistons. The bars thus can be lengthened when the clampingjaws by turning of the arms are to be caused to move towards each otherin order to grip a lightweight concrete element. Loosening of theclamping jaws is brought about by reducing the length of the bars.

The carrier 15 is composed of a great number of sheets 28 placedcrosswise and being of a U-shaped profile. These are mutually connectedby longish beams or plates 29 (FIG. 3), the structure thus becomingrigid lengthwise as well as crosswise. Inside the carrier there isarranged a U-plate 30.

From FIG. 4 is seen that the arms 21 and 23 shown in FIG. 3 to the rightof the lightweight concrete block 1, encompass a pivot 31 common to themboth. Such a pivot 31 is kept in position by holders 32 situated at thelower parts of the sheets 28. From FIG. 4 it is seen, too, that thelower arm 23 consists of two parts or struts 35 and 36, and that upperarm 21 consists of struts 33 and 34. The arms are mounted on the pivotby bearings 37 and 38. It is evident from the above that the pivots 31are rigidly connected to the carrier 15 and that the sole possibility ofmoving the arms 21 and 23 is to swing them. Y

It is otherwise with the arms 20 and 22 shown in FIG. 5. Truly enoughthe lower arms 22 are mounted with hearings on unmovable pivots 39 fixedto holders 40 situated at the lower parts of the sheets 28, but of theupper arms each one is mounted with a bearing around pivot 41 movablerelatively to the carrier 15. The pivot 41 is by a bracket 42 connectedto a synchronizing shaft 43 stretching uninterruptedly along all thelength of the carrier. The synchronizing shaft is possible to turn butthe brackets 42 for all pivots 41 have been fixed to the shaft 43 inquestion, by welding for instance. The shaft as is perhaps best seenfrom FIG. 6 is mounted in hubs 44 fixed to the lower parts of the sheets28. The possibility of turning the shaft in this case is provided byhydraulic cylinders 45 fixed to the carrier 15. The number of thesecylinders may suitably coincide with that of the brackets to get anevenly distributed loading though it would in itself be thinkable to useonly one or few hydraulic aggregates for turning the shaft. The piston45 of the hydraulic aggregate or the rod 46 of the piston is via a hinge47 connected to an upright 48 which, like the bracket, is fixed to theshaft 43 though in this case the connection is perpendicular to thebracket. It will be evident that, when the pistons of the hydraulicaggregates are moving inwards in the cylinders, the shaft 43 will turnanti-clockwise at least by some little distance, while the brackets 42are swinging, causing the pivots 41 with their pertaining arms 20 andclamping jaws 16 to move upwards. At that procedure all the upperclamping jaws 16 move upwards simultaneously according to the invention.FIG. 3 shows now there are rubber wedges 49 on the clamping jaws 16 19to make contact with the lightweight concrete elements.

Now again reference is made to FIG. 1. Here is illustrated that thecarrier 15 is movable vertically by means of two synchronized hydrauliccylinders 50 and 51. The vertical movement of the carrier is controlledby a shaft 52 situated at the top of the carrier and provided both withwheels 53 running in vertical guides 54 on the hanging beams 55 and withcog wheels 56 meshing with straight cog bars 57 on the hanging beams. Onthe carrier there are housings 58 for driving aggregates supplying powerto the different parts of the device.

As will most clearly be evident from FIGS. 2 and 3 the distance betweenthe lower clamping jaws l8 and 19 and the horizontal part of the carrierwhich unites both its downward shanklike parts is at least almost aslong as the height of the block or pile 3. In this case the distancebetween said horizontal part of the carrier and the lower clamping jawsis a little longer than the height of the block.

The device described operates in the following way: A lightweightconcrete block 1, already cured, is brought in, resting on the support2, to a position under the carrier 15 and the vertical position of thelatter is adjusted so as to place the upper pair of clamping jaws 16 and17 above the cut at hand between the topmost element 6a or 8a and thenext one, 6b or 8b, and to place the lower pair 18 19 under the cut ofthe pile in question, i.e. 3 or 4, respectively. See FIG. 2. In thisposition the telescopic bars 24 and 25 are elongated causing theclamping jaws of each pair to bear against the sides of the elements andto grip these. It should be noticed here that in a first stage, forexample, only the clamping jaws a h work those adjacent pile 3 (i-z)being kept apart. When the synchronizing shaft 43 is turned by thehydraulic aggregates 45 far enough to bring the clamping jaws 16 to moveabout mm vertically. This causes the element or course of elements 8a torevolve relatively to elements 8b, the elements thus being separated. Inthe next stage (FIG. 2) the clamping jaws i 2 adjacent pile 3 arebrought to work, those adjacent pile 4(a-h) being kept apart. Thecarrier is lowered far enough to bring the pairs of clamping jaws onboth sides at the level of the upmost cut of the pile 3. The clampingjaws i z are caused to grip the upmost element 6a which revolves and isseparated by turning the synchronizing shaft. In a third stage thecarrier is brought to sink further down in order to bring the clampingjaws a h into their working positions on each side of thenext-to-topmost cut in the pile 4, after which the operations describedare repeated alternately until all elements or courses of elements inboth piles 3 and 4 have been separated. FIG. 3 illustrates an exemplarysubsequent stage. Finally both piles are lifted somewhat from thesupport 2 to make it possible to insert pallets or similar bearingdevices under them, and the piles are brought down to rest on thesepallets, ready to be transported to some suitable place of storing orunloading.

It is evident from the above that all single elements after beingspearated from the block in question remain resting each on the otheruntil all the elements at hand in the pile have been separated. Thereis, thus, no question of removing the elements one after another fromthe pile as they are being spearated, such as has been the case forearlier known methods and devices within the field. The possibility ofkeeping all elements in the pile brings about essential advantages asthe total time consumption for the separating and the arranging of theelements into piles possible to store, is reduced to a minimum, handlingdamages, particularly in the edges of the elements are also manifestlyreduced and to this there is a saving of tools.

In FIG. 8 an example is given of how the described separating device maybe arranged in a plant for the separating and storing of lightweightconcrete elements. In the Figure the totality of the separating deviceis marked with 60. 61 signifies one or more, in this case two, tracks ortransport lines leading from an autoclaving or curing station to atraverser pit 62. In this pit there is arranged a traverser truck 64movable to and fro laterally along rails 63 or similar. On the traversertruck 64 there are rails or transport lines 65 for the support 2 whichis movable longitudinally and carries the piles 3 and 4 of thelightweight concrete elements 6 and 8 respectively. From the separatingdevice 60 there leads a transport line 66 for transporting the support 2in and out. For support most often plane sheets, socalled curing plates,are used. At the side of the traverser pit 62 one or more tracks 67 arearranged for the accumulating of piles. FRom the traverser pit there areone or more tracks 68 leading to one or more stores, e.g. a store 69 forreinforced elements 6 and a store 70 for unreinforced elements 8. 71signifies a store of pallets 72 of suitable sizes. The plant describedmay of course be modified in many ways. Thus the separating device 60may be movable instead of stationary, an economy of transport linesbeing gained. Further the cured elements may be taken into theseparating device via the tracks 66 instead of the tracks 61, the latterthus made away with.

The plant normally functions in the following way: The elements aretaken into the separating device 60 either directly via the tracks 66 orvia the tracks 61 and the traverser truck 64. They are separated in themanner described above being brought to rest on pallets 72. From theseparating device the elements are brought to the stores 69 and via thetraverser truck 64 and the tracks or transport lines 68.

HOwever, it is many times advantageous to accumulate many piles 3 or 4containing elements of the same dimensions to get a support carryingexclusively the same sort of elements before starting the separtingoperation. For that purpose the ranging tracks 67 are used on whichsupports can be kept standing until they have been filled for instancewith unreinforced elements 8 of uniform dimensions. If the plant is runin that way, the alternate operations mentioned previously of theclamping jaws of the carrier, are no more necessary. It is of coursealso possible to separate all elements of one pile before separatingthose of the second one. But then the carrier 15 will have to be broughtup and down two times instead of one.

The hydraulic aggregates belonging to the device here described maysuitably be connected to a special operating panel from which theoperations are controlled in an optional way not shown here, preferablyelectronically.

The advantages of the invented method and device are evident as theclamping forces are evenly distributed along all the length of theelement because of the multitude of the clamping jaws. The number ofthese jaws may suitably be 3 6, preferably 4, per meter. Anotheradvantage is that the device allows for the separating of blocks ofdifierent dimensions. This is particularly important for elements ofdifferent thickness and different profiles, e.g. tongue-and-grooveelements contra plain elements.

It is self'evident that the invention is not limited to that embodimentonly which has been described and shown in the drawings. Thus it ispossible to use carriers movable also horizontally by being suspended toan overhead travelling crane or by wheels at hand on the stand 11'.Instead of hydraulic operating, naturally, other ways of running theplant may come into question, such as pneumatic, mechanic or similarrunning. Many other modifications, too, are possible within the scope ofthe following patent claims:

We claim:

1. A method of separating lightweight concrete elements mutuallydelimited by essentially horizontal cuts but adhering to each other toform at least one block of stacked multiple elements, comprising thesteps of causing one upper pair and one lower pair of mutually oppositeelongate clamping units each to grip in a tonglike manner its respectiveelement of two elements situated on either side of a cut, and impartingto at least one clamping unit of one pair a movement relative to theother pair, thus separating one element from the other, wherein at leastone clamping unit in each pair consists of a multitude of singleclamping jaws which are moved individually and independently of eachother toward the opposite clamping unit to grip the respective elements,thejaws of at least one of the jawtype units being moved simultaneouslyacross the clamping direction during the separating operation to effectsaid separation of one element from the other.

2. A method according to claim 1 wherein each stacked element afterbeing separated is left remaining in the block until essentially allelements lying on top of each other have been separated.

3. A method according to claim 2 wherein the block, after separation ofall its stacked elements, is lifted by lifting the lowermost element soas to lay bare its bottom, and at least one pallet is inserted under theblock, which is then lowered and brought to rest on said pallet.

4. A method according to claim 2 wherein the block comprises at leastone first stack and one second stack horizontally adjacent each otherand containing elements of different dimensions, and wherein in a firststep the topmost element of the first stack is separated and in a secondstep the topmost element of the second stack is separated, after whichthe clamping units are controlled alternately to hold and separateelements of the different piles, the clamping units continuously movingdownwardly until all elements have been separated from each other.

5. A method according to claim 1 wherein the jawtype unit which is movedacross the clamping direction is one unit of the upper pair, and movesrelatively to the other unit of the upper pair and both units of thelower pair so as to effect a pivotal movement of the element beingseparated.

6. Apparatus for separating lightweight concrete elements delimited byessentially horizontal cuts but adhering to each other to form at leastone block of plural stacked elements, said apparatus comprising oneupper pair and one lower pair of mutually opposite elongate clampingunits, means mounting the units of each pair for relative clampingmovement toward each other to have each pair grip in a tong-like mannera respective element of two elements situated on either side of a cut,at least one clamping unit of at least one pair being mounted formovement also across the clamping direction to bring about a pivotalmovement of one element relative to the other for separating saidelements from each other, at least one of the units in the upper as wellas in the lower pair of clamping units comprising a multitude of singleclamping jaws arranged for moving individually and independently of eachother toward the opposite clamping unit during the clamping movement,the clamping jaws of at least one of said jaw-type clamping units beingmovable together and simultaneously across the clamping direction foreffecting said separating of the elements.

7. Apparatus according to claim 6 wherein both units of each pairconsist of a multitude of single clamping jaws, and said across-movableunit comprises one of the units of the upper pair which moves across theclamping direction relative to the other unit of the upper pair andrelative to both units of the lower pair.

8. Apparatus according to claim 7 wherein each of said clamping jaws ismounted on a pivotally mounted arm, the arms for the across-movableupper clamping jaws being mounted on pivots free of adjacent pivots onwhich are mounted the arms for the adjacent lower clamping jaws.

9. Apparatus according to claim 8 wherein the arms of all the clampingjaws which are movable across the clamping direction are connectedmutually by a common synchronizing shaft for effecting the simultaneousmovement of the clamping jaws across the clamping direction.

10. Apparatus according to claim 9 wherein the arms of theacross-movable clamping jaws are connected to the synchronizing shaftvia a linkage for effecting the simultaneous movement of the arms acrossthe clamping direction.

11. A device according to claim 10 wherein the synchronizing shaft isrotatable and said linkage comprises a bracket fixed to thesynchronizing shaft and connected to said pivots around which saidacross-movable arms are mounted so as to move said pivots in said acrossdirection.

12. Apparatus according to claim 1 1 wherein the synchronizing shaft isturned by means of at least one hydraulic motor.

13. Apparatus according to claim 8 wherein the mutually opposite upperclamping jaw arms and the mutually opposite lower clamping jaw arms areconnected at their upper ends above said pivots by piston-andcylinderdevices for effecting said clamping movements.

14. Apparatus according to claim 13 wherein each of the arms consists ofat least two mutually connected adjacent struts, the arm of each upperclamping jaw being mounted between the struts which together form thearm of a lower clamping jaw.

15. Apparatus according to claim 13 wherein the clamping jaws and theirpivotal arms are carried by an elongate carrier of essentially U-shapedcross section, and means mounting the carrier for vertical movement.

16. Apparatus according to claim 15 wherein the distance between thelower clamping jaws and the horizontal part of the U-shaped carrierwhich unites the depending shanks of the U-shape is at least almost aslong as the maximum height of a block of stacked elements to beseparated, such that the lower clamping jaws can grip the lowermostelement of a stack when said carrier is moved downwardly.

* i F i

1. A method of separating lightweight concrete elements mutuallydelimited by essentially horizontal cuts but adhering to each other toform at least one block of stacked multiple elements, comprising thesteps of causing one upper pair and one lower pair of mutually oppositeelongate clamping units each to grip in a tong-like manner itsrespective element of two elements situated on either side of a cut, andimparting to at least one clamping unit of one pair a movement relativeto the other pair, thus separating one element from the other, whereinat least one clamping unit in each pair consists of a multitude ofsingle clamping jaws which are moved individually and independently ofeach other toward the opposite clamping unit to grip the respectiveelements, thejaws of at least one of the jaw-type units being movedsimultaneously across the clamping direction during the separatingoperation to effect said separation of one element from the other.
 2. Amethod according to claim 1 wherein each stacked element after beingseparated is left remaining in the block until essentially all elementslying on top of each other have been separated.
 3. A method according toclaim 2 wherein the block, after separation of all its stacked elements,is lifted by lifting the lowermost element so as to lay bare its bottom,and at least one pallet is inserted under the block, which is thenlowered and brought to rest on said pallet.
 4. A method according toclaim 2 wherein the block comprises at least one first stack and onesecond stack horizontally adjacent each other and containing elements ofdifferent dimensions, and wherein in a first step the topmost element ofthe first stack is separated and in a second step the topmost element ofthe second stack is separated, after which the clamping units arecontrolled alternately to hold and separate elements of the differentpiles, the clamping units continuously moving downwardly until allelements have been separated from each other.
 5. A method according toclaim 1 wherein the jaw-type unit which is moved across the clampingdirection is one unit of the upper pair, and moves relatively to theother unit of the upper pair and both units of the lower pair so as toeffect a pivotal movement of the element being separated.
 6. Apparatusfor separating lightweight concrete elements delimited by essentiallyhorizontal cuts but adhering to each other to form at least one block ofplural stacked elements, said apparatus comprising one upper pair andone lower pair of mutually opposite elongate clamping units, meansmounting the units of each pair for relative clamping movement towardeach other to have each pair grip in a tong-like manner a respectiveelement of two elements situated on either side of a cut, at least oneclamping unit of at least one pair being mounted for movement alsoacross the clamping direction to bring about a pivotal movement of oneelement relative to the other for separating said elements from eachother, at least one of the units in the upper as well as in the lowerpair of clamping units comprising a multitude of single clamping jawsarranged for moving individually and independently of each other towardthe opposite clamping unit during the clamping movement, the clampingjaws of at least one of said jaw-type clamping units being movabletogether and simultaneously across the clamping direction for effectingsaid separating of the elements.
 7. Apparatus according to claim 6wherein both units of each pair consist of a multitude of singleclamping jaws, and said across-movable unit comprises one of the unitsof the upper pair which moves across the clamping direction relative tothe other unit of the upper pair and relative to both units of the lowerpair.
 8. Apparatus according to claim 7 wherein each of said clampingjaws is mounted on a pivotally mounted arm, the arms for theacross-movable upper clamping jaws being mounted on pivots free ofadjacent pivots on which are mounted the arms for the adjacent lowerclamping jaws.
 9. Apparatus according to claim 8 wherein the arms of allthe clamping jaws which are movable across the clamping direction areconnected mutually by a common synchronizing shaft for effecting thesimultaneous movement of the clamping jaws across the clampingdirection.
 10. Apparatus according to claim 9 wherein the arms of theacross-movable clamping jaws are connected to the synchronizing shaftvia a linkage for effecting the simultaneous movement of the arms acrossthe clamping direction.
 11. A device according to claim 10 wherein thesynchronizing shaft is rotatable and said linkage comprises a bracketfixed to the synchronizing shaft and connected to said pivots aroundwhich said across-movable arms are mounted so as to move said pivots insaid across direction.
 12. Apparatus according to claim 11 wherein thesynchronizing shaft is turned by means of at least one hydraulic motor.13. Apparatus according to claim 8 wherein the mutually opposite upperclamping jaw arms and the mutually opposite lower clamping jaw arms areconnected at their upper ends above said pivots by piston-and-cylinderdevices for effecting said clamping movements.
 14. Apparatus accordingto claim 13 wherein each of the arms consists of at least two mutuallyconnected adjacent struts, the arm of each upper clamping jaw beingmounted between the struts which together form the arm of a lowerclamping jaw.
 15. Apparatus according to claim 13 wherein the clampingjaws and their pivotal arms are carried by an elongate carrier ofessentially U-shaped cross section, and means mounting the carrier forvertical movement.
 16. Apparatus according to claim 15 wherein thedistance between the lower clamping jaws and the horizontal part of theU-shaped carrier which unites the depending shanks of the U-shape is atleast almost as long as the maximum height of a block of stackedelements to be separated, such that the lower clamping jaws can grip thelowermost element of a stack when said carrier is moved downwardly.